Constraint Macro

proc parseVars(node: NimNode): (seq[string], NimNode) =
    ## Traverses the AST to find any identifiers
    ## and either replaces them with a constraint
    ## vararg access, or treats them as a Nim
    ## identifier if prefixed `u` or not alphanumeric.
    ##
    ## Return: The Variable names in AST First Occurence Order
    var queue = @[node] # TODO: Change to list, ensure FIFO
    var variables = newTable[string, int]()
    result[1] = queue[0]

    while queue.len > 0:
        let current = queue.pop

        for i, child in current.pairs:
            ## Find any Identifiers on the current Node
            if child.kind == nnkIdent:
                if child.strVal[0] == 'u':
                    ## If tagged as a literal, keep it, but drop tag
                    current[i] = ident(child.strVal.substr(1))
                elif child.strVal.isAlphaNumeric:
                    ## Any untagged identifier is assumed a Variable
                    ## Track its order in the AST
                    if not variables.hasKeyOrPut(child.strVal, variables.len):
                        result[0].add(child.strVal)

                    ## Then replace the Identifier with an Array Access
                    ## corresponding to its location in the constraint
                    current[i] = newNimNode(nnkBracketExpr).add(
                        ident("x"),
                        newIntLitNode(variables[child.strVal])
                    )
            else:
                queue.add(child)


macro constrain*[T](problem: Problem[T], input: untyped): untyped =
    result = newStmtList()

    for child in input:
        let (vars, ast) = parseVars(child)
        result.add ast

    echo result.treeRepr ## No changes occurred